User metadata on workflows/events for user interface usage

[cretz]

What changed?

• Added temporal.api.sdk.v1.UserMetadata containing payloads for summary and details for general metadata use
• Added temporal.api.command.v1.Command.user_metadata for general use (initially only for timers and child workflow)
• Added temporal.api.history.v1.HistoryEvent.user_metadata for general use (initially only for timers)
• Added temporal.api.workflowservice.v1.StartWorkflowExecutionRequest.user_metadata for general use (initially for populating execution config)
• Added temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionRequest.user_metadata for same reason as start
• Added temporal.api.workflow.v1.NewWorkflowExecutionInfo.user_metadata for same reason as start
• Added temporal.api.workflow.v1.WorkflowExecutionConfig.user_metadata for general use (initially for fixed as-of-start summary/details)
• Added temporal.api.sdk.v1.WorkflowMetadata.current_details for the ability to have queryable long-form text representing current details of a workflow
• Removed temporal.api.sdk.v1.WorkflowDefinition.definition because a workflow definition's description isn't best placed on a query (but "current details" is good on the metadata itself)

Why?

• Users need a way to set fixed summary/details when starting a workflow for use by UIs
• Users need a way to have query-obtainable live "current details" for use by UIs
• Users need a way to set a summary when starting a timer for use by UIs
• All of this needs to be encrypted if the user wants
• We need to take into account future user-metadata use

Breaking changes

• Yes for workflow metadata which was only used in JSON form by one SDK (TypeScript) and not even invoked by UI yet

[cretz]

All of the fields are just plain text at the moment, right?

Yes, this is documented on the field

Would be nice to understand what the format is.

Mentioned here, I am intentionally leaving that as out-of-scope for now pending some UI discussions. We should not block this progress on that.